The text thread is the relationship. And it is sitting on someone else's phone.
Your technician gives a customer his cell so they can coordinate the visit. It is efficient. It is also the moment the relationship stops being yours. When he leaves, he takes the thread, the history, the photos and the customer.
This is not a feeling. Alberta courts have priced it. $112,000 in Catch Engineering v Mai, 2023. $111,345 in Stonetile v Castcon, 2010, even though the written confidentiality agreement was too vague to enforce. A 2024 Alberta decision confirmed non solicitation clauses are presumed unenforceable unless narrowly drafted, and that courts will not rewrite a bad one for you.
So the contract probably fails. And if it holds, you are still buying a lawsuit after the damage is done. The only thing that reliably works is making sure there was never a private channel to take.